To design, characterize, and troubleshoot devices and systems (e.g. a device under test (DUT)), engineers need to measure a variety of characteristics of the device signals. To make such measurements, engineers generally use electronic test equipment such as an oscilloscope or network analyzer, a data acquisition (DAQ) instrument, digital multimeter (DMM), etc. and an associated probing system and display.
An oscilloscope is a type of electronic test instrument that allows observation of time-varying electrical signals. During typical operation, an oscilloscope receives an input signal through an oscilloscope probe connected to the DUT and displays the received signal on an electronic display. A test probe is a physical device that connects the test equipment to the DUT.
Oscilloscope probes include passive and active probes. Passive scope probes do not include active electronic parts, such as transistors, so they do not require external power. Active scope probes use a high-impedance high-frequency amplifier mounted in the probe head, and a screened lead. The purpose of the amplifier may be isolation (buffering) between the DUT and the oscilloscope and cable, loading the circuit with only a low capacitance and high DC resistance, and matching the oscilloscope input.
A high voltage probe allows for measuring voltages that would otherwise be too high to measure or even destructive. A high voltage probe reduces the input voltage to a safe, measurable level, e.g. with a voltage divider circuit within the probe body.
Many high voltage applications such as switch mode power supplies, power inverters, motor controllers et cetera have, as part of their function, a rapidly changing voltage that can have a ratio of 100:1, 1000:1, 10,000:1 (or higher) between high and low levels. This voltage is usually accompanied by a rapidly changing current that has the same period. The product of the voltage and current, V*I, of these, signals represents the power lost during power conversion. Typically, to measure these voltages users employ a high voltage differential probe.
Users have traditionally focused their attention to the transitions of the signals from high/low and low/high. However, with faster switching power semiconductors, users would like to accurately measure the voltage during the low portion of the cycle. This traditionally has been very difficult to measure accurately because of the large dynamic range of the voltage. For example, if Vmax is 1000V then the oscilloscope will be set to about 200V/division. At these settings, typical oscilloscope sensitivity is about 10V. The actual voltage during these transitions is typically less than 1V. If the user were to change the sensitivity of the oscilloscope to a higher sensitivity, the measurement may be compromised because the signal will overdrive the oscilloscope inputs and a distorted signal will be displayed. This prevents users from accurately measuring the low (or high) voltages.
In view of the above and other shortcomings of conventional approaches, there may be a general need for approaches and technologies in high voltage level applications to accurately measure and view peak voltages while also providing high sensitivity measurement and display of low level voltages using a large dynamic range probe output.